With a POF-USA P-9X Rail System as an exoskeleton and a M.I.M.S. suppressor at the core of the design, the Coastal Guns 9mm upper receiver is not only functional, it is an absolute overachiever.

The explosion in popularity the black rifle has achieved in the last decade has propelled its appeal far outside the circle of military firearm fans who have embraced it for almost 50 years. No longer a simple and modest 5.56mm rifle with the only options being a different stock and barrel length, some configurations are so far removed from the original design they are barely recognizable as AR-15/M16 family firearms. With this broadened appeal come new innovations as the role of the weapon system continues to evolve, and new accessories and caliber conversions are introduced at lightning speed.

While the use of pistol calibers is certainly not a new concept for this firearm, the latest innovation from Coastal Guns brings it to a level not previously achieved. Manufactured as a complete, suppressed 9x19mm upper receiver, it is a true drop-on unit for anyone with a Colt-style 9mm mag-well adapter and heavy buffer. The short 4.75-inch barrel combined with the M.I.M.S. suppressor brings the overall length far under that of a standard 9mm package and at far less cost than the short D.O.E. style upper receiver.

The barrel is free-floating and is completely shrouded by a POF P-9X Predator Rail system. The top rail extends over 16 inches, from the rear of the upper receiver giving the shooter numerous options for sights and optics, and the three additional rails located at 3, 6 & 9 o’clock allow for several accessory options. The side rails measure 8.5 inches in length and the bottom rail is 7.5 inches.

At the heart of the system is the M.I.M.S. silencer and this is where it really starts to break away from many other suppressed pistol caliber systems. Supplied with the correct thread adapter for this upper receiver, the suppressor is completely removable and can be utilized with several other firearm types. The suppressor is not dedicated or “married” to the upper receiver and with the addition of a new Coastal Guns thread adapter it can be used an almost unlimited number of other guns the owner may have. With the potential for a single suppressor to be used on so many firearms the value is enormous considering the number of transfer fees saved, not to mention the price of several silencers otherwise necessary. (See SAR Vol. 12, No. 8, May 2009 for a complete review of the M.I.M.S. silencer system).

Maximum Modularity

As an exercise in modularity we combined the Coastal Guns 9mm upper receiver, complete with a M.I.M.S. suppressor with an MGI Marck-15 Modular Lower Receiver using their “9mm SMG” mag-well. This MGI lower receiver allows the use of multiple magazine wells so it can be calibrated to the desired caliber and magazine without the use of any adapters or special feeding devices. (See SAR Vol.10, No.8, May 2007 for more information on the MGI Modular Lower Receiver.) The 9mm SMG mag-well uses factory Colt 9mm magazines and lightly modified Uzi magazines. To stretch the level of modularity even more we decided to use a .45 ACP M.I.M.S. suppressor with this system. With the identical overall length and diameter of the 9mm M.I.M.S. suppressor, the fit was perfect and the number of firearms it would adapt to would increase several-fold. Our hypothesis was the increased diameter of the baffle internal diameter would be washed out by the large volume of the suppressor. If it proved effective, the value of the system would skyrocket as the number of firearms compatible with the suppressor multiplied.

Range Time

Range time consisted of several days with almost 1,000 rounds fired by numerous shooters. After a very short break-in period of about 60 rounds, the system started to feed and function perfectly. During the first few magazines while running different types of ammunition we experienced some feeding troubles with hollow-point ammo. After a few magazines everything was running well and not another single function problem of any type was experienced during the remainder of the testing. A short break-in period to get things running smooth is not uncommon with a new firearm or component in the experience of the author.

The first thing we checked was also the most obvious. We were all curious whether the M.I.M.S. .45 ACP suppressor would be adequate for the faster and smaller 9mm round or if we were looking for a little too much in the area of modularity and ignoring too much in the performance area. In the absence of any sound metering equipment we had to rely on the second most important measuring tool: our ears. To have something as a baseline to compare against we first used a M.I.M.S. 9mm suppressor and fired a few different types of ammo. After clearing the firearm and removing the 9mm suppressor we installed the .45 ACP M.I.M.S. suppressor and fired the first few rounds. To our delight it was almost indistinguishable from the 9mm can. We started with the heavier and slower 147-grain ammo and worked our way down to the lighter and much faster 115-grain and even 90-grain ammo. It was also extremely similar in sound levels, and was so comfortable that little or no hearing protection was used throughout the remainder of the testing, even when shooting in an enclosed area. The .45 ACP suppressor would reside on the Coastal Guns upper receiver throughout the remainder of the shooting. Since the testing time overlapped a few local shoots, the system was fired by several people who were all quite impressed in all aspects and all had the same response when they looked at the suppressor engraving. The most frequent question uttered by the shooters was: “This is a .45 can?” Our suppression test was deemed a great success.

The system worked great thus far but just “sounding quiet” and running well wasn’t enough to tell us if it was going to be a useful platform. In practical terms, along with going BANG every time you squeeze the trigger, comes hitting what you need to hit, as well. Since the system is a pistol caliber we set up at approximately 50 yards and tested it with five types of ammunition. We measured some five-shot groups and recorded the muzzle velocity of all. The 9x19mm ammunition tested was: SBR GreenMatch 90-grain Frangible, Wolf 115gr FMJ, Winchester 115-grain FMJ, Atlanta Arms 147-grain Subsonic JHP Match and Winchester 147-grain Subsonic JHP.

Five-round groups were fired from a bench and were recorded as follows: Winchester JHP - 1.935 inches; Atlanta Arms JHP - 2.464 inches; SBR GreenMatch Frangible - 3.250 inches; Wolf FMJ - 3.627 inches and Winchester FMJ - 3.759 inches. Given better weather conditions and more time it would be easy to decrease the size of these groups in the opinion of the author. Acknowledging the tiny 4.75 inch barrel of this system, the accuracy at 50 yards was actually quite impressive when compared to other pistol caliber platforms with similar barrel lengths

The Coastal Guns 9mm upper receiver utilizes a barrel length of only 4.75 inches in length. The addition of the M.I.M.S. suppressor gives it a perceived barrel length of about 15 inches and it doesn’t look grossly short so we thought it was important to mention the following: The Coastal Guns 9mm Upper Receiver can only be used on Title II firearms such as a registered Short Barreled Rifle or registered machine gun. Due to concerns with constructive possession, it is unwise to take possession of a short-barreled upper receiver without having either firearm mentioned above. In these days where transferable machine guns are so expensive, registered short-barreled rifles are gaining in popularity and can still be purchased or manufactured for a reasonable amount of money. (For information on registering your own Short Barreled Rifle see SAR Vol. 12, No. 12, September 2009, page 55.)

Summary

The results of this entire experiment in assembling a solid, reliable, modular rifle exceeded our expectations in all areas. The 9mm barreled upper receiver built and assembled by Coastal Guns and matched with their own M.I.M.S. sound suppressor was well thought out and executed. The addition of the POF-USA P-9X rail system to complete the upper receiver solidified it in areas of practicality, performance and even aesthetics. The fit, finish and function of the entire upper receiver system we tested is simply superb.

The use of the .45 ACP M.I.M.S. suppressor with the system absolutely enhances the ability of the owner to multiply the number of suppressed firearms several-fold. While the number of calibers possible to suppress with this system is far reaching, always contact the suppressor manufacturer prior to using it with any caliber other than that specifically listed. The tiny 4.75-inch barrel makes a fantastic platform for the M.I.M.S. suppressor, as you get the benefit of a suppressor with a huge amount of volume with the benefit of a useful overall length. The suppressor only protrudes 5.5 inches beyond the end of the POF-USA P-9x rail system.

The MGI Military MARCK-15 Modular Lower Receiver seemed like a logical choice to use with this system given the ability to use a mag-well built specifically for the magazine we needed to use with this upper receiver. When combined with their 9mm SMG mag-well the owner can utilize factory Colt 9mm magazines and slightly modified Uzi magazines with no adapters or modifications. The correct magazine for the caliber and the correct magazine for the upper receiver will always assist in enhancing performance variables no longer necessary. The more adapters or custom magazines that are necessary can hinder the performance of a system greatly, and the MGI Lower, the correct magazine and the correct upper receiver came together to function as intended.

Not only can this writer recommend the Coastal/MGI 9mm system to the readers of Small Arms Review magazine, he will be adding this system to his collection at his own expense.